The evolution of the horse is one of the many documented cases of macroevolution.  Although more complex than this simple diagram, the trends can be seen in the diagram.  As the horse evolved, it got larger, it evolved a foot with just a single toe, and the teeth became larger with a longer stronger root reflecting the change in its food from a browsing habit to a grazing habit.

Next to the diagram are fossils of horse teeth.  The tooth on the left is a modern horse, in the middle is a million year old horse, and on the far right is a partial jaw of Mesohippus with two teeth.  Note how small its teeth were compared to the other teeth.